This invention relates to a thrust bearing assembly for a horizontally disposed rotatable shaft.
Many types of thrust bearings have been used in the past for absorbing the axial thrust of a rotatable shaft. Ball, roller or needle bearings have been used with significant success. An example of the use of needle bearings is described in U.S. Pat. No. 3,393,025 to Jenkins, assigned to the General Electric Company, assignee of the present invention. In applications calling for shafts rotating at a relatively high speed on the order of several thousand revolutions per minute this type of bearing may become noisy since under certain loading conditions which occur intermittently during motor operations the needles tend to skid rather than roll. In addition, this type of arrangement tends to be structurally complex. The needle bearing arrangement disclosed by Jenkins, for example, calls for four parts: a spring, two thrust bearing races, and a needle thrust bearing.
Another type of thrust bearing is the simple thrust plate which may be dry or lubricated. The dry thrust plate, due to the absence of lubrication is limited in its usefulness to comparatively low thrust forces and low speed applications. Lubricated thrust plates have proven quite successful for use on vertical shafts where the bearing can be immersed in lubricant so that a dynamic oil film is readily maintained. However, in horizontal shaft applications, maintaining a dynamic oil film on the thrust plate for lubrication is more difficult. One approach to this problem is disclosed in U.S. Pat. No. 3,423,138 to Hardy, assigned to the General Electric Company, assignee of the present invention. Hardy discloses an improved thrust bearing and lubricating system which comprises a rotating thrust plate formed from hardened tool steel, which rotates against a stationary thrust plate of nylon, both bearings being enclosed at least partially in a housing formed from an acetal copolymer for a horizontal rotating shaft application. In the Hardy arrangement axial thrust is transmitted from the rotating thrust bearing mounted within the housing to a stationary thrust bearing within the housing and from the stationary thrust bearing to a spherical support bearing. The Hardy arrangement requires the bearing housing to retain lubricating oil around the bearings so as to maintain the protective lubricating film between the rotating thrust bearing and the stationary bearing surfaces.
Bearings formed from a porous composition such as a sintered or powdered metal composition which can be saturated with oil, or formed from a self-lubricating material such as graphite, have less stringent lubrication requirements than metal alloy bearings. However, these composition materials, while strong in compression, tend to be relatively weak in tension. Thus, the press fitting of such a bearing with the shaft to rotate with the shaft may subject the bearing to excessive tensile stress, causing the bearing to break during assembly or in operation. Use of a simple thrust bearing loosely carried on the shaft for random rotation is undesirable because such a bearing may intermittently rotate against the wrong bearing surface, causing the bearing to deteriorate or break apart. In order to use powdered metal or graphite thrust bearings, a thrust bearing assembly including means for rotating the bearing with the shaft which does not subject the bearing to excessive tension is required.
Thus, it is desirable to provide an improved thrust bearing assembly for use with a horizontally disposed rotating shaft which approaches the structural simplicity of the dry thrust plate yet which provides satisfactory lubrication for high speed application.
Accordingly, it is an object of this invention to provide an improved thrust bearing assembly for a rotatable shaft.
It is another object of this invention to provide an improved thrust bearing assembly for a rotatable shaft which is relatively quiet and relatively structurally simple.
It is another object of this invention to provide an improved thrust bearing assembly for use with a horizontally disposed shaft employing a porous powdered metal thrust bearing.
It is another object of this invention to provide an improved thrust bearing assembly for use with a horizontally disposed shaft employing a thrust bearing formed from a self-lubricating composition.
It is another object of this invention to provide an improved thrust bearing assembly for use with a horizontally disposed rotating shaft employing a thrust bearing formed from a powder metal or graphite composition which rotates with the shaft.